1. Field of the Invention
The present invention relates generally to light-emitting semiconductor devices capable of emitting light having a wavelength of about 1.3 microns to about 1.55 microns. More particularly, the present invention relates to such light-emitting devices incorporating metamorphic buffer layers.
2. Description of the Related Art
The telecommunications industry desires light sources capable of emitting light having a wavelength of about 1.3 microns to about 1.55 microns. These wavelengths correspond, respectively, to minimum dispersion and minimum loss in conventional glass optical fibers and would thus enable improved long distance and high speed optical communication.
Edge emitting and vertical cavity surface emitting lasers (VCSELs) that include active regions fabricated from indium-containing semiconductor material systems of appropriate composition, such as InGaAsP and AlInGaAs material systems, are capable of operating at 1.3 microns and 1.55 microns. Such active regions, however, typically cannot be grown lattice-matched to GaAs. Growth of such indium-containing materials on GaAs typically results in dislocations and other crystal defects that degrade the performance of the device. Consequently, light-emitting semiconductor devices capable of emitting light at about 1.3 microns to about 1.55 microns are typically grown lattice-matched to InP substrates. Unfortunately, InP substrates are generally smaller, more expensive, and more fragile than GaAs substrates.
In addition, VCSELs typically include one or more distributed Bragg reflectors (DBRs) designed to reflect light emitted by the active region. The Bragg reflectors provide optical feedback to the active region. Unfortunately, DBRs formed from material systems that can be lattice-matched to InP typically perform poorly compared to conventional GaAs/AlAs DBRs lattice-matched to GaAs.
What is needed is a light-emitting device integrating a semiconductor structure capable of emitting light having a wavelength of about 1.3 microns to about 1.55 microns with a GaAs substrate.
A light-emitting device in accordance with an embodiment of the present invention includes a GaAs substrate, a light-emitting structure disposed above the substrate and capable of emitting light having a wavelength of about 1.3 microns to about 1.55 microns, and a buffer layer disposed between the substrate and the light-emitting structure. The composition of the buffer layer varies through the buffer layer such that a lattice constant of the buffer layer grades from a lattice constant of the substrate to a lattice constant of the light-emitting structure.
The buffer layer comprises InxAl1xe2x88x92xAs with 0xe2x89xa6xxe2x89xa61, in one embodiment. Such a buffer layer is formed, for example, by supplying to the substrate a flux of aluminum, a flux of arsenic, and a flux of indium, and varying a ratio of the flux of aluminum and the flux of indium as the buffer layer grows. In one implementation, the substrate is maintained at a temperature between about 380xc2x0 C. and about 420xc2x0 C. while the buffer layer is formed.
In one embodiment, the light-emitting device further includes a GaAs/AlAs distributed Bragg reflector disposed between the substrate and the buffer layer. In this embodiment, the composition of the buffer layer varies such that a lattice constant of the buffer layer grades from a lattice constant of the distributed Bragg reflector, typically lattice-matched to the GaAs substrate, to a lattice constant of the light-emitting structure.
In another embodiment, the light-emitting device includes a second GaAs/AlAs distributed Bragg reflector and a second buffer layer. The composition of the second buffer layer varies such that a lattice constant of the second buffer layer grades from a lattice constant of the light-emitting structure to a lattice constant of the second distributed Bragg reflector.
Light-emitting devices in accordance with embodiments of the present invention may exhibit improved mechanical, electrical, thermal, and/or optical properties compared to similar light-emitting devices grown on InP substrates.